Lead frame and its manufacturing method

ABSTRACT

A leadframe is plated with palladium only to a surface of a metal plate on which semiconductors elements are to be mounted and a surface of the metal plate to be placed on a substrate, and is not plated with palladium to lead portions, pad portions, other portions except for the surfaces to be plated and the side surface, of the leadframe, thereby, the amount of use of palladium is reduced to minimum and a cheap leadframe can be provided.

TECHNICAL FIELD

[0001] The present invention relates to a leadframe to be used forsemiconductor devices and manufacturing method of the same.

BACKGROUND ART

[0002] Conventionally, a leadframe is manufactured in such way that apattern of the leadframe is formed from a metal plate by etching orpress processing, then, after palladium plating is carried out to thewhole surface of it, semiconductor elements are mounted on thepredetermined position, and then, after sealing with resin, cutting iscarried out by using a die etc. Finally, separate chips are produced.Such products are in practical use as electronic parts as IC chips.

[0003] In recent years, in a specification of the leadframe, the use ofcoating by solder plating containing lead has ceased in consideration ofthe influence on environment, and palladium plating to the whole surfaceof the leadframe has been used. However, since palladium is an expensivemetal material, there is a problem of raising the product cost by usingpalladium plating to the whole surface.

[0004] Accordingly, the main object of the present invention is toprovide a cheaper leadframe by minimizing the amount of palladium used.

[0005] Other object of the present invention is to provide amanufacturing method of leadframe by which the fault of the leadframe iseliminated.

DISCLOSURE OF THE INVENTION

[0006] In order to attain the above-mentioned objects, the leadframeaccording to the present invention is characterized in that, in aleadframe which is formed from a metal plate, palladium plating ispartially carried out only to necessary and minimum portions on whichsemiconductor elements are to be mounted, portions to bond gold wiresand portions to be soldered of a surface to be placed on a printedcircuit board.

[0007] Besides, the leadframe according to the present invention ischaracterized in that, in a leadframe which is formed from a metalplate, palladium plating is carried out only to a surface on whichsemiconductor elements are to be mounted and a surface to be placed on aprinted circuit board, and that the palladium plating is not carried outto lead portions formed, pad portions, other portions except for thesurfaces to be plated and its side surface.

[0008] Besides, the leadframe according to the present invention ischaracterized in that, in a leadframe which is formed from a metalplate, palladium plating is carried out only to necessary and minimumportions of a surface on which semiconductor elements are to be mountedand a surface to be placed on a printed circuit board, the palladiumplating is not carried out to lead portions formed, pad portions, otherportions except for the portions of the surfaces to be plated and itsside surface.

[0009] According to the present invention, much cheaper leadframes canbe provided since the area to be plated with palladium can be minimized,in comparison with the conventional leadframe in which palladium platingis carried out to the whole area.

[0010] Further, in the manufacturing method of a leadframe according tothe present invention, a leadframe material is provided by forming ametal plate, and then, palladium plating is carried out only to portionswhich are necessary and minimum for mounting of semiconductor elementsof the leadframe material, and then, the plating is carried out toportions to bond gold wires and necessary and minimum portions to besoldered of a surface to be placed on a printed circuit board, of theleadframe material.

[0011] Besides, in the manufacturing method of a leadframe according tothe present invention, a leadframe material is provided by forming ametal plate, and then, palladium plating is carried out only to asurface of the leadframe material on which semiconductor elements are tobe mounted and then, the plating is carried out only to a surface of theleadframe material to be placed on a printed circuit board, while theplating is not carried out to lead portions, pad portions, otherportions except for the surfaces to be plated and the side surface ofthe leadframe material.

[0012] Besides, in the manufacturing method of a leadframe according tothe present invention, a metal plate is prepared to form a leadframe,and then, a resist layer is formed on the both sides of the metal plate.And after having made a mask (e.g. a mask, which is closely attached tothe surface of the resist layer, for exposing light, developing andplating) with a desired pattern of the leadframe on the surface of theresist layer, the surface of the exposed metal plate is plated, whereinthe plated layers containing at least palladium plated layer are formedand then the mask is stripped, and a resist layer is again formed on thewhole both sides of the plate. Then, after exposing light by using themask with a predetermined pattern and developing are carried out, anetching mask is obtained. And then, the shape of lead portions, padportions and other portions are formed by etching.

[0013] Further, in the manufacturing method of a leadframe according tothe present invention, a metal plate is provided to form a leadframe byforming the metal plate and then a resist layer is formed on the bothfront and back surfaces of the metal plate. And after having made a mask(e.g. a mask, which is closely attached to the surfaces of the resistlayer for exposing light, developing and plating) with a desired patternof the leadframe on the surface of the resist layer, the surface of theexposed metal plate is plated, wherein plated layers containing at leastpalladium plated layer is formed. Then, the resist layer is removed,etching of the metal plate is carried out by using the plated layer asan etching resist, wherein the etching is stopped before the portions ofthe metal plate which is necessary to be etched are penetrated by theetching. And then, the back surface of the metal plate is masked with atape, and the portion of the metal plate, which is necessary to beetched, is penetrated by carrying out etching again. Thus, the relationof positions of a number of lead portions etc. can be kept individuallyand independently by the tape.

[0014] Further, in the manufacturing method of a leadframe according tothe present invention, a metal plate is provided to form a leadframe andthen a resist layer is formed on the both sides of the metal plate. Andafter having made a mask (e.g. a mask for carrying out etching which isclosely attached to the surface of the resist layer for exposing light,and then developing) with a desired pattern of the leadframe on thesurface of the resist layer, the exposed metal plate portion is removedby the etching and the pattern of leadframe is formed. Then, the bothfront and back surfaces of the leadframe are plated so as to form aplated layer containing at least palladium layer.

[0015] Further, in the manufacturing method of a leadframe according tothe present invention, a metal plate is provided to form a leadframe anda resist layer is formed on the both front and back surfaces of themetal plate. And after making a mask (e.g. a mask for carrying outplating which is closely attached to the surface of the resist layer andto which light is exposed and then developing is carried out) with adesired pattern of the leadframe on the surface of the resist layer, thesurface of the exposed metal plate is plated, thereby, plated layerscontaining at least palladium plated layer are formed. Then the resistlayer is removed and etching of the metal plate is carried out by usingthe plated layer as an etching resist. Thus, patterns of a number oflead portions, pad portions and others are formed.

[0016] According to the methods described above, the leadframe which isnot only cheaper but also does not cause such fault as missing of lead,breakage of resin etc., as seen in the conventional leadframe can beprovided since it is good enough to cut only the resin portion at thetime when the leadframe is cut into small chips by using the cutting ordicing device etc., after semiconductor elements are mounted on thepredetermined position on the leadframe and sealing is made by resinbecause the metal portions to be cut has already dissolved by theetching.

[0017] These and other objects as well as the features and advantages ofthe present invention will become apparent from the following thedetailed description referred to the accompanying drawings.

BRIEF EXPLANATION OF DRAWINGS

[0018]FIG. 1 is a flowchart illustrating an embodiment of manufacturinga lead frame according to the present invention.

[0019]FIG. 2 is a flowchart illustrating another embodiment ofmanufacturing a lead frame according to the present invention.

[0020]FIG. 3 is a flowchart illustrating the other embodiment ofmanufacturing a lead frame according to the present invention.

[0021]FIG. 4 is a flow chart illustrating further other embodiment ofmanufacturing a lead frame according to the present invention.

[0022]FIG. 5 is a schematic side view illustrating the positionalrelation between a lead frame manufactured by the method of the presentinvention and a substrate as a printed circuit board.

BEST MODE FOR CARRYING OUT THE INVENTION

[0023] Embodiment 1

[0024]FIG. 1 is a flowchart illustrating an embodiment of themanufacturing method of leadframe according to the present invention. Inthe FIG. 1, 1 is a plate of copper or similar material for forming aleadframe. 2 is a dry film mounted on the front and back surface of themetal plate 1. 3 is a glass mask which is put on the dry film 2 placedon the surface of the metal plate 1, and which forms a leadframe pattern3 a by using a light shielding agent. 4 is a glass mask which is put onthe dry film 2 placed on the back surface of the metal plate 1, andwhich forms a leadframe pattern 4 a on symmetrically opposite side tothe leadframe pattern 3 a with respect to the metal plate 1 by using thelight shielding agent. 5 and 6 are glass masks which form predeterminedshading patterns, and 7 are a plurality of etching liquid injectionnozzles which are disposed oppositely at both sides of the metal plate1.

[0025] Next, the manufacturing process of the leadframe will beexplained in turn. First, as shown in FIG. 1A, the dry film 2 working asphotoresist is placed on the whole front and back surfaces of the metalplate 1. Then, the glass masks 3 and 4 which have the leadframe patterns3 a and 4 a are put on the front and back surfaces at the state ofpositioning of the pattern. And such both surfaces are exposed by theultra violet ray through the glass masks 3 and 4.

[0026] After exposure, the glass masks 3 and 4 are removed and the metalplate 1 with dry film is soaked into the developing solution fordevelopment. Thus only the portions of the dry film 2 exposed by theultra violet ray, i.e., portions which are necessary to be plated withpalladium, such as portions to which gold wires are bonded and portionsfor mounting thereon semiconductor elements are removed as shown in FIG.1B.

[0027] Next, this is put into a plating tub, and as shown by partiallyenlarged scale in FIG. 1C, necessary plating of nickel (Ni), palladium(Pd) or gold (Au) etc. is carried out in turn for necessary portions. Inthis way, the metal plate 1 with the plated layer 1 a of thecross-sectional configuration as shown in FIG. 1D can be obtained bystripping the dry film 2.

[0028] The dry film 2 is again placed on the whole both front and backsurfaces of the metal plate 1 with the plated layer 1 a which wasobtained in the way as described above. Then, as shown in FIG. 1E, theglass masks 5 and 6 on which the pattern is formed so as to shade onlythe plated portions are put on the film 2 and the both sides are againexposed by the ultra violet ray. Then, as explained in FIG. 1B, thedevelopment is carried out, and the metal plate 1 with the plated layer1 a of the cross-sectional configuration as shown in FIG. 1F isobtained.

[0029] As shown in FIG. 1G, etching is carried out by spraying etchingliquid through the injection nozzles 7 on the both surfaces of the metalplate 1 with plated layer 1 a. By this etching, the metal portions onwhich plating is not carried out is dissolved and removed. Finally, bystripping the dry film 2, one frame of the leadframe which has thecross-sectional configuration as shown in FIG. 1H, that is, on whichplating was carried out only to the necessary minimum portion isobtained.

[0030] Each process shown in FIGS. 1A to 1H is carried out continuouslyby conveying a metal plate having the length including a plurality offrames on an appropriate conveyer and each frame of the leadframe iscompleted after being cut at the final stage of the process. As it isevident by the explanation above, consequently, palladium plating iscarried out only to necessary portions of the front and back surfaces ofeach leadframe.

[0031] Embodiment 2

[0032]FIG. 2 shows a flowchart illustrating another embodiment of themanufacturing method of leadframe according to the present invention. InFIG. 2, the same reference numerals in FIG. 1 are used to thesubstantially same components and portions, the explanation of thereference numerals are omitted. Since each process shown in FIGS. 2A,2B, 2C and 2D is the same as each process shown in FIGS. 1A, 1B, 1C and1D as it is clearly seen by comparison with FIG. 1, the explanation ofsuch process is omitted, with respect to each process shown after FIG.2E, the explanation will be made.

[0033] As shown in FIG. 2E, the etching is carried out by spraying theetching liquid through the injection nozzles 7 to the both sides of themetal plate 1 with the plated layer 1 a. Such etching is carried outuntil the metal of the portion where the plating is not carried outbecomes extremely thin in consequence of such metal having been almostdissolved and removed.

[0034] After a tape 8 is attached, as shown in FIG. 2F, to the wholesurface of the one side of the metal plate 1 with the plated layer 1 awhich was obtained in this way, the etching is again carried out byspraying the etching liquid through the injection nozzles 7 from theside to which the tape 8 is not attached as shown in FIG. 2G. Thus, theextremely thin metal portions to which the plating is not carried out(unnecessary portions, such as tie bars for connecting lead portions andhanging leads which are to be cut out after the assembling process) arecompletely dissolved and removed. In this case, the remained metalportions namely, such necessary portions as portions on whichsemiconductor elements are to be mounted, pad portions and lead portionswhere the plating has been carried out are certainly held withoutcollapsing relative positions by the tape 8, as shown in FIG. 2H.

[0035] Embodiment 3

[0036]FIG. 3 shows a flowchart illustrating still another embodiment ofthe manufacturing method of leadframe according to the presentinvention. In FIG. 3, the same reference numerals in FIG. 1 are used tothe substantially same components and portions, the explanation of thosenumeral references is omitted. Since each process shown in FIGS. 3A and3B is the same as the process shown in FIGS. 1A and 1B as it is clearlyseen in comparison with FIG. 1, the explanation of such processes isomitted, with respect to each process shown after FIG. 3C, theexplanation will be made.

[0037] As shown in FIG. 3C, the etching is carried out by spraying theetching liquid through the injection nozzles 7 on both sides of themetal plate 1 on which the dry film 2 remains corresponding to theleadframe pattern. Such etching is carried out until the metal plate 1comes to have penetrated holes as a consequence of dissolution andremoval of the metal of portions on which the dry film 2 do not exist,as shown in FIG. 3D. Thus the dry film 2 is stripped from the bothsurfaces of the metal plate 1 having the holes. In this way, theleadframe material with cross sectional configuration as shown in FIG.3D is manufactured.

[0038] On the necessary portions on the front and back surfaces of theleadframe material (metal plate 1) obtained in this way, the nickel (Ni)plating, palladium (Pd) plating, and gold (Au) plating are carried out,respectively, as shown by an enlarged scale in FIG. 3E and then aleadframe is completed. That is to say, as shown in FIG. 3F, at first,the nickel (Ni) plating is carried out to the whole surface of the frontand back surfaces of the leadframe as a ground layer, and then as shownin FIG. 3G below, the palladium (Pd) plating is carried out only to thenecessary minimum portions for semiconductor mounting portions, portionsto bond gold wires and portions to be soldered of the surface to be on aprinted circuit board. Finally, as shown in FIG. 3H, the gold (Au)plating is carried out to the both sides of the front and the backsurfaces of the leadframe and then a leadframe is completed. Thus,according to the present invention, the amount of the expensivepalladium used can be at a minimum, and the finished product of aleadframe is much cheaper as compared with the conventional leadframe.

[0039] Embodiment 4

[0040]FIG. 4 shows a flowchart of still another embodiment of themanufacturing method of leadframe according to the present invention.The same reference numerals used in FIG. 1 are given to thesubstantially same components and portions and the explanation aboutthem is omitted. The explanation of FIGS. 4A to 4D is omitted since eachprocess is the same as those of FIGS. 1A to 1D as it is evident bycomparison with FIGS. 1A to 1D. The processes shown after FIG. 4E willbe explained.

[0041] This embodiment differs from the first embodiment in such pointthat the product is manufactured by the etching, that is, by sprayingthe etching liquid through the injection nozzles 7 on both sides of themetal plate obtained in FIG. 4 D on which the plating was completedwithout carrying out the second light exposure and the development.According to this embodiment, the product can be provided much cheaper.

[0042] As explained above, according to the present invention, theleadframe which is not only much cheaper but also does not cause faultsuch as missing of lead and breakage of resin in comparison with theproduct by the conventional method can be provided.

1. A leadframe formed from a metal plate comprising: a portion formounting thereon a semiconductor element, portions to be bonded withgold wires, and portions to be soldered of the surface to be placed on aprinted circuit board, wherein palladium is plated only to necessary andminimum part of said portions of said leadframe.
 2. A leadframe formedfrom a metal plate comprising: a first surface for mounting thereon asemiconductor element, a second surface to be placed on a printedcircuit board, and shaped lead portions, wherein palladium is platedonly to said first and second surfaces, while palladium is not plated toother portions except for said first and second surfaces and the sidesurface of said leadframe.
 3. A leadframe formed from a metal platecomprising: a first surface for mounting thereon a semiconductorelement, a second surface to be placed on a printed circuit board, andshaped lead portions, wherein palladium is plated only to necessary andminimum part of said first and second portions, while palladium is notplated to other portions except for said necessary and minimum part andthe side surface of said leadframe.
 4. A method of manufacturing aleadframe, comprising the steps of: preparing a leadframe material byforming a metal plate, plating palladium to necessary and minimumportions of said leadframe material on which semiconductor elements areto be mounted, and plating palladium to portions to bond gold wires andnecessary and minimum portions to be soldered of a surface to be placedon a printed circuit board, of said leadrame material.
 5. A method ofmanufacturing a leadframe, comprising the steps of: preparing of aleadframe material by forming a metal plate, plating palladium only to asurface of said leadframe material on which semiconductor elements areto be mounted, and plating palladium only to a surface of said leadframematerial to be placed on a printed circuit board, excepting leadportions, pad portions, other portions except for said surfaces to beplated and the side surface, of said leadframe material.
 6. A method ofmanufacturing a leadframe, comprising the steps of: preparing aleadframe material by forming a metal plate, plating palladium only tonecessary and minimum portions of a surface of said leadframe materialon which semiconductor elements are to be mounted, and plating palladiumonly to necessary and minimum portions of a surface of said leadframematerial to be placed on a printed circuit board, excepting leadportions, pad portions, other portions except for said surfaces to beplated and the side surface, of said leadframe material.